The invention relates to a method for selecting a servicing routine for servicing for an inkjet print head and more particularly to the field of selecting a servicing routine for servicing of an inkjet print head in a manner that reduces the amount of time which is necessary for servicing.
Inkjet printers are widely used in many private and occupational computer applications. In particular, color inkjet printers are of great importance. Since e.g. digital photographing is becoming more and more popular, there is an increasing demand for a cheap color printer which provides a high picture quality.
An inkjet printer has the disadvantage that its print head can easily dry out if the printer is not used for a period of time. The drying out occurs because parts of the liquid ink stored in the print heads evaporate. This evaporation causes the performance of the print head pens to be reduced. The process of drying out first causes a reduced print quality. A further drying out can also lead to a complete failure of the inkjet printout. In that case the print head pens might irreversible be damaged so that a complete replacement of the print head might be necessary.
Therefore Hewlett Packard™ has introduced a method to prevent or at least to slow down the evaporation of the ink stored in the print head. One effective way to reduce the ink evaporation is to cap the print head pens during the period in which the ink jet printer is not active.
However capping of the print head pens and the necessary removing of the capping prior to executing a print job reduces the quality of the first printout after the capping of the print head pens has been removed. To improve this printout quality servicing routines for cleaning the print head pens after removing the capping and prior to executing a print job have been introduced. These servicing routines are called Out Of Cap servicing routines.
Table 1 shows the Out Of Cap servicing routines which are currently employed in a Hewlett Packard inkjet printer. Depending on the time the ink jet printer has been sitting idle before executing a print job and depending on the status of the power cycle of the ink jet printer, servicing routines Out Of Cap A, Out Of Cap B, Out Of Cap C, Out Of Cap D, Out Of Cap E and Out Of Cap F are initiated.
TABLE 1Overview over currently employed servicing routines, trigger events forthe servicing routines and approximate time duration for performing theservicing routines.servicingapproximateroutinetrigger eventtime durationOutOfCapAPrior to executing a print job and after the0.3secprinter was sitting idle for<60 minOutOfCapBPrior to executing a print job and after the0.3secprinter was sitting idle for>60 min and <2 daysOutOfCapCPrior to executing a print job and after the3.1secprinter was sitting idle for>2 days and <7 daysOutOfCapDPrior to executing a print job and after the3.1secprinter was sitting idle for>7 days and < 14 daysOutOfCapEPrior to executing a print job and after the8.7secprinter was sitting idle for >14 days ORafter the printer has gone through a CleanPower CycleOutOfCapFPrior to executing a print job after the15.8secprinter has gone through aDirty Power Cycle
In the following the actions which are carried out when the currently employed servicing routines are executed are briefly described. The servicing routines OutOfCapA and OutOfCapB involve only a “spitting” in order to clear the nozzles. In this context “spitting” means that some drops of ink are ejected from the nozzles. The servicing routines OutOfCapC and OutOfCapD include at first a spitting of ink drops, second a dry wiping of the print head and third again a spitting of ink drops. Dry wiping means that the print head is wiped without using a solvent. By contrast the servicing routine OutOfCapE includes a wet wiping of the print head after the first spitting of ink drops and prior to the second spitting of ink drops. Wet wiping means that the print head is wiped using a solvent. The servicing routine OutOfCapF combines both the OutOfCapD and the OutOfCapE servicing, i.e. the following sequence of actions is carried out: spitting of ink drops, dry wiping the print head, again spitting of ink drops, wet wiping the print head and a last spitting of ink drops. The amount of ejected ink is different for the different servicing routines, i.e. the execution of a particular servicing causes a predefined number of ink drops to be ejected from the nozzles.
The actions which are carried out in the different OutOfCap servicing routines are briefly summarized in Table 2.
TABLE 2Summary of the actions which are carried out when the different servicingroutines are executed.servicing routineactionsOutOfCapAspitting only to clear the nozzlesOutOfCapBspitting only to clear the nozzlesOutOfCapCspitting, dry wiping, spittingOutOfCapDspitting, dry wiping, spittingOutOfCapEspitting, wet wiping, spittingOutOfCapFspitting, dry wiping, spitting, wet wiping, spittingactioncomment on actiondry wipingwiping the print head without solventwet wipingsolvent assisted wipingspittingspitting for the different routines varies in thenumber of drops of ink ejected from the nozzles
The status of the power cycle of the inkjet printer is classified by two different notations. In this context “clean power cycle” means that the printer had been switched off during a state in which the inkjet printer had been at rest, i.e. during switching off the printer the printer had not executed a print job and the print head had been at rest, and later on the printer was switched on. By contrast “dirty power cycle” means that before switching on the printer the inkjet printer had been switched off during a state in which the printer and in particular the print head had not been at rest.
Each Out Of Cap servicing routine requires a certain amount of time for performing the cleaning procedure. The corresponding time durations are also listed in the right column of table 1.
While the quality of the first inkjet printer printout after removing the capping of the print head pens can effectively be increased due to the usage of print head servicing routines, the speed of executing the print jobs which require a afore print head servicing is reduced.
In particular after the printer has been switched on after a clean power cycle there is no way to determine how long the print head pens have been capped. Therefore it is not possible to choose the proper servicing routine. In that case the most aggressive servicing routine Out Of Cap E is initiated in order to ensure a high printout quality (compare table 1).
In the following we will only attend the case that the printer has gone through a clean power cycle. As one can easily see from table 1 the currently employed procedure of initiating Out Of Cap servicing routines has the drawback that in most cases the time of executing a printout is delayed for a period which is longer than necessary. Only when the printer has been sitting idle for a period longer than 14 days the currently employed procedure of initiating Out Of Cap servicing routines initiates by chance the proper servicing routine and no time is wasted before executing a print job. If the ink jet printer has been sitting idle for a period shorter than 14 days the first printout is delayed because time is wasted for performing unnecessarily accurate servicing routines which last longer than the requisite servicing routine for performing sufficient cleaning of the print head pens (compare third column in table 1).
One object of the present invention is to provide a method for reducing the amount of time which is necessary for performing inkjet print head servicing routines prior to executing a print job after the inkjet printer has gone through a clean power cycle.